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Saturday, August 29, 2009

AUGUST 27 - Is quantum mechanics messing with your memory?

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Is quantum mechanics messing with your memory?

For all we know we may live in a world in which windows un-break and cold cups of coffee spontaneously heat up, we just don't remember. The explanation is quantum entanglement

Broken glass

A physicist has claimed that glass can un-break – but quantum entanglement prevents our brains from recording the event. Photograph: David Levene

Imagine if a cold cup of coffee spontaneously heated up as you watched. Or a cracked pane of glass suddenly un-broke. According to physicist Lorenzo Maccone at the Massachusetts Institute of Technology, you see things like this all the time – you just don't remember.

In a paper published last week in Physical Review Letters, he attempts to provide a solution to what has been called the mystery of "the arrow-of-time".

Briefly, the problem is that while our laws of physics are all symmetrical or "time-reversal invariant" – they apply equally well if time runs forwards or backwards – most of the everyday phenomena we observe, like the cooling of hot coffee, are not. They never seem to happen in reverse.

We have a statistical law that describes these everyday phenomena called the Second Law of Thermodynamics. This law tells us that the "entropy" or degree of disorder of a closed system never decreases. Roughly speaking, a process in which entropy increases is one where the system becomes increasingly disordered. Windows break, thereby increasing disorder, but they will not spontaneously unbreak. Gases will disperse but not spontaneously compress.

However, entropy describes what happens with large numbers of particles. We presume that it must arise from what happens with individual particles, but all the laws that govern the behaviour of individual particles are time-reversal invariant. This means that any process they allow in one direction of time, they also allow in the other.

So why will your coffee spontaneously cool down, but not heat up?

Maccone's solution is to suggest that in fact entropy-decreasing events occur all the time – so there is no asymmetry and no associated mystery about the arrow of time.

He argues that quantum mechanics dictates that if anyone does observe an entropy-decreasing event, their memories of the event "will have been erased by necessity".

Maccone doesn't mean that your memories will never form in the first place. "What I'm pointing out is that memories are formed and then are subsequently erased," he tells me.

When you observe any system, according to Maccone, you enter into a "quantum entanglement" with it. That is, you and the system are entangled and cannot properly be described separately.

The entanglement, Maccone says, is between your memory and the system. When you disentangle, "the disentangling operation will erase this entanglement, namely the observer's memory". His paper derives this conclusion mathematically.

While we cannot remember our cups of coffee re-heating, and hence cannot study them, Maccone thinks that entropy-decreasing events like that must happen.

"If transformations that increase the entropy do occur – and we know that they do – by symmetry we should expect also transformations that decrease the entropy – but we cannot see them."

I'm not convinced that Maccone has solved the dilemma of the arrow of time, and I'm not alone.

One problem is that, as he acknowledges, he cannot prove that entropy-decreasing events occur. Rather, he shows that if they do, we won't remember them.

Concerns about symmetry lead him to conclude that they must in fact happen. However, it is statistically very (very, very very) unlikely that the entropy of a macroscopic system will decrease.

It's all down to the way particles move around. In a gas, for example, there are many fewer ways in which the particles can be in a lower entropy state than there are ways for them to be in a higher entropy state. So the most likely state either before or after is one of higher entropy – simply because there are many more such states for the system to occupy.

Importantly, the statistics of entropy do not predict an asymmetry, because they suggest entropy should neither decrease towards the past nor decrease towards the future.

The mystery of the arrow of time is that entropy only increases towards the future. Put another way, why does entropy actually decrease towards the past, despite what the statistics predict?

Maccone says that "we should expect" entropy decreases towards the future since they occur towards the past. But the statistics show us that we should expect no such thing. It is enormously surprising that they happen towards the past and it would be doubly surprising if they happened towards the future. Symmetry is not a reason to expect what we know is statistically extremely unlikely.

Huw Price, head of the Centre for Time at the University of Sydney, thinks Maccone is simply trading one mystery for another.

"The proposal to explain the thermodynamic arrow in terms of the [quantum] effects of observers has an obvious flaw," he says. "It doesn't explain why all observers have the same orientation in time ... Why don't some observers remember what we call the future, and accumulate information towards what we call the past?"

A standard way of explaining why observers like us remember the past is by appealing to thermodynamics – the fact that entropy is increasing. This explanation is unavailable to Maccone since his theory takes that thermodynamic fact to depend on the existence of observers. Such an explanation, for Maccone, would thus be circular.

If Price is right, then Maccone has explained one temporal asymmetry at the expense of creating another that is equally hard to explain.

What's more, Price thinks that Maccone has made a hidden asymmetrical assumption. He argues that the quantum correlations Maccone relies on must be assumed to happen only in one temporal direction and not the other. "But that's just assuming the conclusion he wants to derive."

Whether or not Maccone has solved the mystery of the arrow of time is unclear. But to tell the truth, it would suit me just fine if my cold cup of coffee heated back up all on its own. I don't even care if I remember it happening or not.

Michael Slezak is a freelance journalist and teaches the philosophy of science at the University of Sydney, Australia

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How to Digitally Record/Video a UFO sighting:

Como registar digitalmente ou gravar um vídeo de um avistamento de um UFO:

Stabilize the camera on a tripod. If there is no tripod, then set it on top of a stable, flat surface. If that is not possible lean against a wall to stabilize your body and prevent the camera from filming in a shaky, unsteady manner.

Estabilize a camera com um tripé. Se não tiver um tripé, então coloque-a em cima de uma superfície estável. Se não for possível, então encoste-se a uma parede para estabilizar o corpo e evitar que a camera registe de maneira tremida e instável.

Provide visual reference points for comparison. This includes the horizon, treetops, lampposts, houses, and geographical landmarks (i.e., Horsetooth Reservoir, Mt. Adams, etc.) Provide this in the video whenever is appropriate and doesn’t detract from what your focus is, the UFO.

Forneça pontos visuais de referência para comparação. Isso inclui o horizonte, cimo das árvores, postes de iluminação, pontos de referência geográficos (como o Reservatório de Horsetooth, Mone Adams, etc) Forneça esses pontos no vídeo sempre que for apropriado e não se distraia do que é o seu foco, o UFO/a Nave.

Narrate your videotape. Provide details of the date, time, location, and direction (N,S,E,W) you are looking in. Provide your observations on the weather, including approximate temperature, windspeed, any visible cloud cover or noticeable weather anomalies or events. Narrate on the shape, size, color, movements, approximate altitude of the UFO, etc and what it appears to be doing. Also include any unusual physical, psychological or emotional sensations you might have. Narrate any visual reference points on camera so they correlate with what the viewer will see, and thereby will be better able to understand.

Faça a narração do vídeo. Forneça pormenores sobre a data, hora, local e direcção (Norte, Sul, Este, Oeste) que está a observar. Faça observações sobre as condições atmosféricas, incluindo a temperatura aproximada, velocidade do vento, quantidade de nuvens, anomalias ou acontecimentos meteorológicos evidentes. Descreva a forma, o tamanho, a cor, os movimentos, a altitude aproximada onde se encontra o UFO/nave, etc e o que aparenta estar a fazer. Inclua também quaisquer aspectos pouco habituais de sensações físicas, psicológicas ou emocionais que possa ter. Faça a narração de todos os pontos de referência visual que o espectador irá ver e que, deste modo, será capaz de compreender melhor.

Be persistent and consistent. Return to the scene to videotape and record at this same location. If you have been successful once, the UFO sightings may be occurring in this region regularly, perhaps for specific reasons unknown, and you may be successful again. You may also wish to return to the same location at a different time of day (daylight hours) for better orientation and reference. Film just a minute or two under “normal” circumstances for comparison. Write down what you remember immediately after. As soon as you are done recording the experience/event, immediately write down your impressions, memories, thoughts, emotions, etc. so it is on the record in writing. If there were other witnesses, have them independently record their own impressions, thoughts, etc. Include in this exercise any drawings, sketches, or diagrams. Make sure you date and sign your documentation.

Seja persistente e não contraditório. Volte ao local da cena e registe o mesmo local. Se foi bem sucedido uma vez, pode ser que nessa região ocorram avistamentos de UFOs/naves com regularidade, talvez por razões específicas desconhecidas, e talvez possa ser novamente bem sucedido. Pode também desejar voltar ao mesmo lugar a horas diferentes do dia (durante as horas de luz)para ter uma orientação e referência melhor. Filme apenas um ,inuto ou dois em circunstâncias “normais” para ter um termo de comparação. Escreva tudo o que viu imediatamente após o acontecimento. Logo após ter feito o registo da experiência/acontecimento, escreva imediatamente as impressões, memórias, pensamentos, emoções, etc para que fiquem registadas por escrito. Se houver outras testemunhas, peça-lhes para registar independentemente as suas próprias impressões, pensamentos, etc. Inclua quaisquer desenhos, esbolos, diagramas. Certifique-se que data e assina o seu documento/testemunho.

Always be prepared. Have a digital camera or better yet a video camera with you, charged and ready to go, at all times. Make sure you know how to use your camera (and your cell phone video/photo camera) quickly and properly. These events can occur suddenly, unexpectedly, and often quite randomly, so you will need to be prepared.

Esteja sempre preparado, Tenha sempre uma camera digital, melhor ainda, uma camera vídeo consigo, carregada e pronta a usar sempre que necessário. Certifique-se que sabe como lidar com a sua camera (ou com o seu celular/camera fotográfica) rápida e adequadamente. Esses acontecimentos podem acontecer súbita e inesperadamente e, por vezes, acidentalmente, por isso, necessita estar preparado.

Look up. Be prepared. Report. Share.

Olhe para cima, Esteja preparado, Relate, Partilhe.



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